In an amplifier comprising an output driver with a first output stage and a second output stage, where an input signal is applied non-inverted to the first output stage and inverted to the second output stage, usually denominated as a class-D amplifier/driver, an input signal (typically an audio-signal) is transformed into an output signal capable of being reproduced into the original signal on an external load, usually a speaker or the like. In the basic operation of a class-D amplifier/driver, an incoming signal is converted e.g. by a pulse-width or pulse-code modulator or the like into a high-frequency rectangular wave, the average value of which tracks the original signal. The rectangular wave is fed into an output stage which provides level shifting and splits the signal into a high/low driving signal. The driving signal is filtered to remove the switching noise, providing an averaged output to drive a load such as a speaker.
The output of a differential class-D amplifier/driver oscillates between two extremes to represent an analog signal. These two extremes are built by having 1-0 or 0-1 at the output. For example an amplifier powered by a 5V voltage has at one extreme a first output pin at a voltage of 5V and a second at a voltage of 0V. On the other extreme, the first output pin is at a voltage of 0V and the second at a voltage of 5V.
A resistive or capacitive load applied to the amplifier always has a voltage of ±5V at its boundaries and thus enables the load to draw a lot of current.